But when scientists thaw the cells for use in the lab, less than 1 percent awake from their frigid slumber and assume their undifferentiated state. This 'blank slate' form is characteristic of stem cells and essential for the basic science required before the promising cells are ready for the clinic. So scientists are required to place the few survivors in culture and painstakingly tend to them for weeks before new colonies are abundant enough to conduct experiments.

"Human embryonic stem cells have a very low survival rate following cryopreservation, which causes several problems," says Sean Palecek, a University of Wisconsin-Madison professor of chemical and biological engineering.

Not only does that low rate make working with human embryonic stem cells time and labor intensive, but - because so few survive freezing - it may also mean that natural selection is altering the stored cells in unknown and undesired ways, he says.

But now Palecek, along with colleagues Juan de Pablo and Lin Ji, are putting the finishing touches on a new method for preserving and storing the finicky cells. The work, presented today (March 30) at a meeting of the American Chemical Society, promises to greatly amplify the number of cells that survive their enforced hibernation, that remain undifferentiated and that are more readily available for research. What's more, with more survivors, genetic variability becomes less of an issue.

By freezing the cells attached to a gel matrix instead of suspended in solution, and adding the chemical trehalose - a disaccharide or sugar that some animals and microbes produce to protect cells and survive in dry, low-temperature conditions - the Wisconsin team was able to increase
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30-Mar-2004